1. Field of the Invention
The present invention relates to shaping glass sheets and particularly to a method of fabricating apparatus for shaping glass sheets by a press bending operation which apparatus is relatively inexpensive to fabricate, yet capable of producing sample patterns of bent glass sheets within precise tolerances. Though the present invention originated to solve problems existing in the shaping of glass sheets, it is understood that the principles of the present invention may be employed for shaping sheet material other than glass when the sheet material is softened sufficiently for shaping.
Glass sheets or plates have been bent by supporting the sheet to be bent between a pair of glass shaping members while at a temperature sufficiently high to be deformable by pressurized contact between a pair of glass shaping members having major complementary shaping surfaces conforming to the shape desired for the bent glass. In the past, the glass shaping members were of either solid metal or refractory members.
Glass shaping members fabricated of solid metal are costly to fabricate. The fabricated parts are not suitable to produce patterns other than the one for which they are originally made, except for a family of glass sheets of uniform radius of curvature but of different sizes. Furthermore, an expensive and time consuming grinding operation is needed to correct the shape of any high spots on the shaping surface and it is necessary, in order to correct for any low spot relative to the shaping surface of the shaping member, to grind a considerable portion of the shaping surface to compensate for the low spot.
2. Description of Patents of Interest
U.S. Pat. No. 3,367,764 to Seymour provides glass shaping apparatus of the press bending type that is easily adjustable to change its shape in the event glass sheets are bent slightly out of tolerance without requiring grinding of the shaping surface or dismantling of the entire apparatus. In addition, the Seymour patented apparatus is capable of simple adjustment to produce several different configurations that are not too dissimilar from one another.
Each glass shaping member of an illustrative embodiment of the apparatus patented to Seymour comprises a relatively flexible shaping plate of metal having a pressing face whose shape approximates that of the shape desired for the glass sheet after bending. The relatively flexible shaping plate extends substantially continuously throughout substantially its entire extent and has sufficient rigidity to resist deformation during pressurized engagement against a heat-softened glass sheet.
The patented apparatus also comprises a relatively rigid member in the form of a rigid, more massive metal plate having an area at least substantially coextensive with that of the relatively flexible metal plate located in spaced relation behind said relatively flexible metal plate and of a thickness of approximately 1/2 inch. Attachment means is distributed throughout the extent of the relatively flexible metal plate and the relatively rigid metal plate for connecting the plates in spaced relation to one another, for insuring positive alignment of the central portion of the shaping plate to the corresponding portion of the rigid plate while permitting the shaping plate to expand thermally without distorting from its desired local configuration, and for making slight alterations in the shape of the relatively flexible metal plate without altering the configuration of the relatively rigid metal plate. The space between the shaping plate and the rigid plate permits access to adjust the attachment means. Such adjustment changes the local contour of the shaping plate by altering the distance between the shaping plate and the rigid plate in the vicinity of the attachment means that is adjusted. The rigid plate of the Seymour apparatus is fixed in spaced relation to a rigid mounting plate. The latter is attached to a piston for movement therewith.
In the fabrication of adjustable press bending apparatus of the type patented by Seymour in the aforementioned patent, one end of each attachment means is rigidly attached by welding or soldering to the rear surface of the flexible metal plate while the other end portion extends through an opening in the relatively rigid plate and is secured to said plate by adjustable securing members, each comprising a threaded shaft extending through an opening in the rigid plate and adjustment nuts threaded onto the shaft on each side of the rigid metal plate.
The holes drilled in the rigid metal plate to receive the end portions of the attachment means are located in proper alignment with the locations where the adjustable securing members are secured to the rear face of the flexible metal plate whose pressing face has a shape that conforms to a particular pattern. However, these locations of the holes in the rigid plate may be unsuitable for use with a flexible metal plate whose pressing face has a shape that conforms to another pattern. Hence, when production requirements for a particular pattern are ended and production begun on a new pattern, it becomes necessary to store the flexible metal plate with the rigid metal plate until the production program requires producing the particular pattern again. Storage space becomes a problem in a plant producing many different patterns of curved glass windows for autos and other uses. Furthermore, the cost of the relatively massive rigid metal plates adds considerably to the cost of the inventory of press bending molds that must be stored when not in use. Also, the mass of the rigid metal plates necessary to insure sufficient rigidity to insure that the flexible metal plates rather than the rigid metal plates change their shape when the attachment means are adjusted must necessarily be so great as to impose a burden on the apparatus that actuates the press bending molds to move between a retracted position and a glass engaging position. Hence, the maximum speed at which the press bending molds move between these positions must be controlled to limit inertia problems. This may increase the time needed for each bending cycle, thus reducing the rate at which bent glass sheets can be produced successfully.
U.S. Pat. No. 3,871,857 to Claassen provides a press bending apparatus particularly suitable for use in shaping heat-softened glass sheets that has an adjustable pressing mold as in the Seymour patent or an adjustable pressing frame, but is lighter in weight and has a rigid member adapted for use with several different flexible metal plates whose shapes conform approximately to different production patterns. Storage space needed for unused press bending mold structures comprising a flexible metal plate is reduced considerably and the total mass of the press bending mold structure stored (relatively flexible metal plate or frame with the press face plus that of the relatively rigid reinforcing member and attachment means) is considerably less than that of a similar press bending apparatus conforming to the Seymour patent.
The Claassen patent obtains these benefits by using an open grate instead of a heavy plate as a reinforcement for the relatively flexible plate provided with the press face. The open grate reinforcement is thicker than the reinforcement plate of the Seymour patent but has less weight because of the open areas throughout the grate.
The use of a thicker but lighter metal grate as a reinforcing member for an adjustable shaping plate as in the Claassen patent avoids the need for punching holes in the reinforcing plates to receive the adjustable attachment means that attach the rigid member to a shaping plate or frame and those needed to receive the mounting bolts that attach the rigid plate to the mounting plate, which latter plate is attached to move with a piston rod. Furthermore, adjusting the shaping plate or frame is easier with a reinforcing grate rather than a solid reinforcing plate because an operator can see what he is doing more easily through the apertures of a grate when he adjusts the shaping face of a press bending member provided with a grate rather than a solid plate as its reinforcing member. Furthermore, it is unnecessary to dismount the reinforcing grate together with the shaping plate or frame from attachment to the mounting plate whenever production changes require a change in the flexible metal shaping plate or frame. It is only necessary to remove the flexible metal shaping plate or frame conforming to the old production pattern from the grate and attach a flexible metal shaping plate or frame conforming to the new production pattern to the grate, which latter remains permanently attached to the mounting plate attached to the actuating piston.
Despite the aforesaid improvements mentioned for the apparatus covered by the Claassen patent, the fabrication of press bending molds for shaping glass sheets remained an expensive undertaking, particularly in the production of several different sample patterns which automotive stylists require for evaluation prior to deciding which of the patterns will be needed for mass production purposes. The extraordinary expense involved in fabricating different press bending molds for each evaluated pattern is further increased by the fact that when the prior art techniques of attaching the attachment means to the rear surface of the relatively flexible, metal shaping plate or frame by welding or soldering, the previous smoothness of the curve defined by the shaping plate becomes distorted. In order to restore the surface smoothness of the shaping plate in the vicinity of the attachment weld or solder point, it becomes necessary to grind localized portions of the shaping plate, inspect the ground portion and repeat the grinding and inspecting until surface smoothness is restored. Such procedures as grinding and measuring repeatedly for each weld or solder point is extremely time consuming and the expense is not justified, particularly in the final adjustment of the shaping plates for a press bending mold that is destined for limited use to produce at most only a small number of evaluation samples of a bent glass pattern that are eliminated when the car styling is decided.
Other patents relating to molds to press bend glass sheets to shape that include a flexible shaping plate and a spaced reinforcement plate reported in a novelty search of the present invention include U.S. Pat. No. 3,512,953 to Roseman, U.S. Pat. No. 3,819,351 to Shaffer and Plank, U.S. Pat. No. 4,052,185 to Kolakowski, U.S. Pat. Nos. 4,052,188 and 4,082,530 to Seymour and U.S. Pat. No. 4,108,624 to Claassen. Also, the novelty search reported U.S. Pat. No. 4,018,589 to Egbert and McDonald and U.S. Pat. No. 4,071,345 for showing the use of aluminum instead of other metals and materials in glass sheet shaping molds. None of these patents teach the glass sheet bending art how to eliminate localized distortion where attachment means are bonded to the rear surface of an adjustable shaping plate or frame.